Defines the radius of the element's corners.
默认属性
border-radius: 0;
Removes any border radius.
border-radius: 20px;
You can use pixel values.
border-radius: 50%;
You can use percentage values. In this example, the radius starts halfway through each border.
border-radius: 20px 50%;
If you set two values, the first one is for the top and bottom borders, the second one for the left and right borders.